fix(audit): harden module isolation and fix post-extraction drift

Fix 5 broken FQCN references (runtime errors) where core pages referenced
non-existent MintyPHP\Service\Audit\AuditMetadataEnricher and SystemAuditService.
Add AuditMetadataEnricherInterface with NullAuditMetadataEnricher fallback so
deactivating the audit module no longer crashes core edit pages.

Move audit search resources from core Search*Provider files into the module
via a new AuditSearchResourceProvider implementing the existing
SearchResourceProvider contract. Add module-specific purge permissions
(audit.api.purge, audit.imports.purge) replacing core ABILITY_ADMIN_SETTINGS_UPDATE.

Also fixes: session key prefix convention, hardcoded English string, $_SERVER
superglobal fallback, and manifest schema drift (i18n_path, group in ui_slots).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/Architecture/AuditModuleIsolationContractTest.php

@@ -17,8 +17,10 @@ final class AuditModuleIsolationContractTest extends TestCase
         ));
 
         $allowed = [
+            'AuditMetadataEnricherInterface.php',
             'AuditRecorderInterface.php',
             'ImportAuditInterface.php',
+            'NullAuditMetadataEnricher.php',
             'NullAuditRecorder.php',
             'NullImportAudit.php',
             'NullUserLifecycleAudit.php',